The present invention is directed to a detent assembly for a rotatable knob, and more particularly, to a magnetic detent assembly for providing audible feedback during the rotation of an occlusion adjustment knob on a peristaltic pump.
Peristaltic pumps are commonly utilized in medical applications. For instance, such pumps are often employed during cardiovascular surgery to facilitate circulation of blood between a patient and a heart-lung machine. Other common medical uses are the transfer of blood between a patient and a kidney dialyzer, and intravenous feeding of IV solutions. Generally, peristaltic pumps are simply structured, generate a constant flow, and employ disposable tubes as a member for fluid transfer.
Peristaltic pumps are relatively simple in construction and typically include a housing having rollers which progressively compress a flexible tube at spaced intervals against an arcuate surface or raceway so as to flatten or locally reduce the cross-sectional area of the tube. In this manner, fluid leading to the flexible tube is continuously forced through the flexible tube by one or another of the rollers as it proceeds along the flexible tube over the arcuate surface or raceway.
A conventional roller pump 10, as shown in FIG. 1, comprises a drive mechanism 14 furnished with a drive shaft 12, a rotating shaft 16 which rotates according to the rotation of drive shaft 12, and a hollow pump head 20 fixed to a housing 18 to which drive mechanism 14 is attached. This pump head 20 integrally incorporates a bearing block 24 through which rotating shaft 16 is inserted and rotatably supported by a pair of bearings 22 and a stator 26 arranged on the upper portion of bearing block 24. On the upper surface of stator 26 is formed a recess 28 through which the upper end of rotating shaft 16 is protruded. While this recess 28 is radially and outwardly spaced at a certain distance from the outer circumferential surface of rotating shaft 16, its inner circumferential surface 28a is coaxial with rotating shaft 16.
A rotor assembly 30 is attached to the upper portion of rotating shaft 16 in such a way as to be placed inside recess 28 of stator 26 and to stay opposite the inner circumferential surface 28a thereof. This rotor 30 is fixed to rotating shaft 16 through a bolt 32, and is so constructed as to integrally rotate along with rotating shaft 16. On the outer circumferential surface of rotor 30, at least one roller 34 is arranged so as to rotate about its own axes. A tube 36 which is filled with blood or other fluid material is placed between rotor 30 and stator 26. Tube 36 is clamped between respective rollers 34, which are attached to rotor 30, and inner circumferential surface 28a of stator 26, thereby maintaining tube 36 in a closed state at the point at which it is clamped.
Thus, in a conventional roller pump 10, rotor 30 is rotated by the rotational motion of rotating shaft 16 driven by drive mechanism 14, and the clamped portions of tube 36 move according to the revolution of rollers 34 around rotating shaft 16. Therefore, fluid inside tube 36 is transferred according to the revolution of rollers 34. The rate of rotation of the rotating shaft 16 and hence the rollers 34 is normally adjustable so that the pumping rate of the fluid within tube 36 can be adjusted. However, the pumping rate can also be adjusted by adjusting the degree to which the rollers compress the flexible tube. This can be done in peristaltic pump assemblies by providing an adjustment mechanism for adjusting the distance between the axes of the rollers and hence the distance between the roller surface and the inner circumferential surface 28a of stator 26. Another important reason for peristaltic pumps to be adjustable in this fashion is that the compressibility, size, and other qualities of the flexible tube can vary considerably.
A rotor assembly 30xe2x80x2 having an adjustable occlusion capability, as shown in FIG. 2, comprises a rotor hub 40, and opposing roller slides 42, each of which carries at least one roller 34 on the outer circumferential surface thereof. The roller slides 42 are extended or retracted from the hub 40 by turning the knob 44 on the top of the rotor hub. The extension or retraction of the roller slides thereby changes the occlusion of the flexible tube within the peristaltic pump. The knob 44 is usually provided with a detent assembly or some other type of mechanism which provides an audible feedback or signal as the knob is being rotated.
Typical detent assemblies disposed in the occlusion adjustment knob 44 include spring loaded balls or plungers that ride against a plate or disk with a series of slots or shallow holes. This type of detent mechanism provides both tactile and audible feedback as the plate moves over the spring loaded ball or plunger. However, both the tactile and audible feedback can be significantly reduced to the point of being nearly undetectable if there is significant resistance to the movement of the plate or disk. For instance, when there is a significant resistance to the rotation of the adjustment knob, such as caused by increased compression of the flexible tube, for instance, the feel and sound of a spring loaded detent may be almost undetectable.
In addition, the metal-to-metal contact between the plate and the spring loaded ball or plunger tends to create wear which in turn may affect the precise positioning required by the spring loaded ball within the slots or shallow holes of the plate. More particularly, the corners of the notches or holes in a spring loaded detent plate or disk will tend to become rounded, changing the feel and sound of the detent as the plate wears under contact. Commercially available spring loaded ball plungers often have a 0.025 inch or less range of travel. The sound and feel of a spring loaded detent can also be quite sensitive to the force of the spring on the ball. Because of the sensitivity and limited range of travel, the use of a spring loaded ball can require that the tolerances on the mechanical assembly be rather tight in order to assure that the ball rides properly and consistently on the moving plate or disk.
Accordingly, there is a need in the art for a reliable detent assembly for providing an audible indication of rotation of a knob, which is not compromised when resistance to movement is encountered and which does not require the precise positioning of the prior art.
A preferred embodiment of the present invention overcomes these drawbacks of the prior art by providing a roller pump comprising a stator, a rotor assembly disposed within the stator, the rotor assembly including a rotor hub, a first roller slide and a second roller slide slidingly disposed within the rotor hub, and each of the roller slides supporting a roller. An occlusion adjustment knob is provided for adjusting a radial position of the first and second roller slides and a magnetic detent assembly provides an audible indicator as the occlusion adjustment knob is rotated. A further preferred embodiment of the roller pump comprises a detent ring, with the magnetic detent assembly being disposed proximate to the detent ring. In a preferred embodiment, the magnetic detent assembly includes a base member having two sealed enclosures, each of the enclosures including a magnetically attractable member and a magnet. Preferably, the magnetically attractable member is a sphere, such as a steel ball.
A further preferred embodiment of the present invention is directed to a knob assembly comprising a rotatable knob having an under surface and a top surface for gripping by a user, a notched plate rotatable with the rotatable knob and arranged proximate to the under surface of the rotatable knob, and a magnetic detent assembly disposed substantially stationary proximate to the notched plate. Rotation of the rotatable knob and the notched plate over the magnetic detent assembly thus provides a user with an audible indicator of rotation.
A still further preferred embodiment of the present invention provides a magnetic detent assembly comprising a base member having a top surface and a bottom surface, at least one magnetically attractable member disposed in a recess in the base member, and at least one magnet disposed in the base member. The at least one magnetically attractable member is movably contained in the recess between the top surface of the base member and the at least one magnet.